The popping noise you hear when you put food in the microwave is caused by a phenomenon known as "thermal expansion." When food is heated in the microwave, the water molecules within the food absorb the microwave energy and start to heat up. As the water molecules heat up, they turn into steam.
The popping noise occurs when the steam inside the food rapidly expands and escapes from the food. This sudden release of steam creates a popping or cracking sound. It's similar to the sound you may hear when water is heated on a stove and reaches its boiling point.
Different foods have different moisture content and composition, which can affect the intensity of the popping noise. For example, foods with high water content, such as vegetables or fruits, are more likely to produce noticeable popping sounds compared to drier foods like bread or baked goods.
It's important to note that while popping noises are common and generally harmless, some precautions should be taken to ensure safe microwave usage. When heating foods with a tendency to pop, it's recommended to cover them with a microwave-safe lid or microwave-safe plastic wrap to prevent potential splattering or mess. Additionally, always follow the instructions provided by the food manufacturer for microwave heating to ensure proper cooking and safety.